5.17.
TROUGH CONSTRUCTION
169
beeswax or dental wax. The lower edges of the trough should grip the
knife well enough so that it will stay in place momentarily after fitting
the two together. Then a small piece of wax is laid inside of the trough
against the metal, and the metal heated judiciously with a small flame.
The wax then melts, and surface tension pulls wax between glass and
metal to complete a seal (Fig. 19b). One trough, of course, can be used
over and over again if moderately heavy sheet metal is used. Or metal
foil can be used and then discarded, this having the advantage that it can
be cut and trimmed with scissors. Probably the chief justification for
using metal is that when properly cleaned it will not contaminate the
acetone solution. Cleaning, of course, means that grease films are eliminated, including those that might come from fingerprints.
A "trough" of sorts can be made most easily simply by drawing a line with
a wax glass-marking pencil across the back of the knife. The line is parallel
to the edge and about J in. behind it. This will confine a drop or two of
acetone solution to the edge region of the knife and the sections can be
floated on this surface. Naturally, one cannot cut very many sections
before the surface is covered, and there is no good way of picking them up
except directly on a screen grid. Working in such close quarters, one is
apt to damage the knife edge in doing this, and with so little fluid there
are added dangers of contamination. Furthermore, the acetone evaporates
rapidly. For these various reasons the method is not recommended for
general use, but it is rapid and convenient when only a few sections are
needed, perhaps for test purposes, and when one has no interest in conserving the knife edge.
On occasion one wishes to move sections about within the trough.
This may be done with a sharp toothpick having a bent tip. The tip
should be wet in advance in the acetone solution, and introduced under
the surface of the trough fluid. The bent tip is then delicately brought
up underneath the section to be moved until it touches. It is then possible
to move the ribbon and, as importantly, disengage it afterwards.
FIG. 19. (a) To the right, a commercially made bronze metal trough, fitted to a
glass knife, in proper position, with a bit of dental wax laid inside ready to be heated
to make the seal. A wooden match indicates size. To the left a similar trough is shown
unfolded to indicate its pattern, (b) Heating the metal of the trough with a microburner (or even a match) causes the wax to melt. Surface tension pulls it between
metal and glass to form a tight seal.
TROUGH CONSTRUCTION
169
beeswax or dental wax. The lower edges of the trough should grip the
knife well enough so that it will stay in place momentarily after fitting
the two together. Then a small piece of wax is laid inside of the trough
against the metal, and the metal heated judiciously with a small flame.
The wax then melts, and surface tension pulls wax between glass and
metal to complete a seal (Fig. 19b). One trough, of course, can be used
over and over again if moderately heavy sheet metal is used. Or metal
foil can be used and then discarded, this having the advantage that it can
be cut and trimmed with scissors. Probably the chief justification for
using metal is that when properly cleaned it will not contaminate the
acetone solution. Cleaning, of course, means that grease films are eliminated, including those that might come from fingerprints.
A "trough" of sorts can be made most easily simply by drawing a line with
a wax glass-marking pencil across the back of the knife. The line is parallel
to the edge and about J in. behind it. This will confine a drop or two of
acetone solution to the edge region of the knife and the sections can be
floated on this surface. Naturally, one cannot cut very many sections
before the surface is covered, and there is no good way of picking them up
except directly on a screen grid. Working in such close quarters, one is
apt to damage the knife edge in doing this, and with so little fluid there
are added dangers of contamination. Furthermore, the acetone evaporates
rapidly. For these various reasons the method is not recommended for
general use, but it is rapid and convenient when only a few sections are
needed, perhaps for test purposes, and when one has no interest in conserving the knife edge.
On occasion one wishes to move sections about within the trough.
This may be done with a sharp toothpick having a bent tip. The tip
should be wet in advance in the acetone solution, and introduced under
the surface of the trough fluid. The bent tip is then delicately brought
up underneath the section to be moved until it touches. It is then possible
to move the ribbon and, as importantly, disengage it afterwards.
FIG. 19. (a) To the right, a commercially made bronze metal trough, fitted to a
glass knife, in proper position, with a bit of dental wax laid inside ready to be heated
to make the seal. A wooden match indicates size. To the left a similar trough is shown
unfolded to indicate its pattern, (b) Heating the metal of the trough with a microburner (or even a match) causes the wax to melt. Surface tension pulls it between
metal and glass to form a tight seal.